Recuperator for gaseous media for use in an industrial gas burner
Patent Information
- Application Number
- PCT/DE2026/100329
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-03-14
- Filing Date
- 2026-03-14
- Publication Date
- 2026-09-17
Smart Images
Figure DE2026100329_17092026_PF_FP_ABST
Abstract
Description
[0001] KPSP 009 WO T6.docx
[0002] recuperator for gaseous media
[0003] Use in an industrial gas burner
[0004] The invention relates to a recuperator for gaseous media for use in an industrial gas burner, comprising the features of the preamble of claim 1.
[0005] Such a recuperator is known from DE 10326951 A1. The heat exchanger wall, which meanders in cross-section, forms partial channels with a multitude of grooves on its inner and outer circumferences. This increases the surface area available for heat exchange. One disadvantage of the known recuperator is its considerable weight, with a wall thickness of 6 mm in the meandering section. This large wall thickness reduces the flow volume, considering the imaginary annular space between the smallest inner diameter and the largest outer diameter of the recuperator as the volume available for heat exchange. Furthermore, the heat exchanger surface area is no longer scalable in the disclosed configuration, as a higher degree of folding reduces the developed length of the partial channels.Furthermore, it is stated that not the entire gas volume flows through the grooves of the meandering heat exchanger wall, but rather that only a secondary flow is formed there, while a primary flow continues, as with traditional recuperators, to flow over the fins in a cylindrical flow chamber. This not only reduces the heat exchange between the media, but also, with regard to the external exhaust gas recirculation channel, leads to soot and other deposits accumulating in the recesses as the gas flows over the fins.
[0006] EP 3974760 A1 describes a tubular recuperator for a recuperative burner, whose almost entire internal volume is filled with a complex channel system formed by triple-periodic minimal surface areas (TPMS). This results in a very large effective heat exchanger surface area. In addition to the inlet and outlet openings, further openings are provided on the outer circumference, which can be covered during operation and facilitate cleaning of the external exhaust gas channel. However, apart from a central bore, there is insufficient internal space to allow the passage of multiple combustion gas lines and / or probes with sensors. Cleaning the other, internal flow channel is also difficult, as it lacks openings on its inner circumference.
[0007] The object of the invention is to create a large effective heat exchanger surface in a recuperator of the type mentioned above, while at the same time increasing the interior space in the center.
[0008] This problem is solved by a recuperator for gaseous media for use in an industrial gas burner with the features of claim 1.
[0009] According to the invention, a heat exchanger wall forms a heat exchanger microstructure with a large surface area. As in the prior art, each of the two counter-flowing main channels is divided into a plurality of sub-channels in an initial region and rejoined in a final region. The initial and final regions can be located directly at the end faces of the recuperator; however, they can also be arranged at a distance from them, so that the division into sub-channels does not extend over the entire length of the tubular recuperator, but at least over a substantial portion of it.
[0010] Furthermore, a key approach to increasing the effective heat exchanger surface area involves designing a meandering heat exchanger wall cross-section, creating a deep fin structure. This structure is then further enhanced by incorporating point-like passages that connect two adjacent channels carrying the same medium. These passages are circumferentially linked by two wall sections of a fin and simultaneously by the intervening channel carrying the other medium. The passages are not openings leading into a directly adjacent channel, but rather small tunnels that traverse the adjacent channel without opening towards it. They only open again at the next-but-one channel belonging to the same flow path. At the same time, the tunnel-like passage remains narrow enough on the outside that it does not completely obstruct the channel it crosses.
[0011] In the heat exchanger microstructure according to the invention, at least essential flow paths are formed in each of the two counter-flowing main channels:
[0012] - a largely linear longitudinal flow along the course of the sub-channels over the length of the recuperator; and
[0013] - a transverse flow in the circumferential direction through the passages located one after the other at an axial position on a circular path.
[0014] In a preferred embodiment, a third flow direction can be superimposed on the two aforementioned flow directions, in which the radial positions of the passages change over the length of the recuperator, so that a flow direction along the Z-axis (central axis) is superimposed on a radial flow direction from inside to outside or vice versa.
[0015] Such structures can only be manufactured using additive manufacturing processes, making it possible to seal each of the sub-channels to the inner or outer circumference. Preferably, however, the heat exchanger microstructure, in addition to the inlet and outlet openings for the channels on its end faces, has further openings on its outer circumference that can be covered by a removable outer recuperator jacket. The same applies to the inner circumference, where further openings can also be provided that can be covered by a removable inner recuperator jacket. After removing the recuperator jackets, the openings are exposed, thus facilitating cleaning.
[0016] The advantage of easier cleaning is already apparent with only a few openings. It is particularly preferred to leave the partial channels of at least one flow channel, and preferably the partial channels of both main channels, completely open to the inner or outer circumference, so that the partial channels appear as deep grooves after the recuperator jackets have been removed.
[0017] The heat exchanger microstructure according to the invention is preferably based entirely or substantially on a complex channel system formed by triple-periodic minimal surfaces (TPMS), in which the return channel and the feed channel are each divided into a plurality of small sub-channels at least in a partial region of their length, which are joined together again in an end region.
[0018] Preferably, the TPMS heat exchanger microstructure is generated in a polar coordinate system whose center lies on the central axis of the tubular recuperator. The cylindrical centering enables the formation of a multitude of sub-channels with optimized heat exchange surface areas, which can be integrated within a heat exchanger wall with low radial expansion.
[0019] According to the invention, it is provided that at least in axial sections of the heat exchanger microstructure, adjacent sub-channels of the same main channel are connected to each other by several point penetrations, which connect two adjacent sub-channels of the same main channel and extend through a sub-channel of the other main channel without opening or closing upon passing through to this other sub-channel.
[0020] Tunnel-like cross-connections are thus created between adjacent sub-channels, extending through an intervening rib of the meandering heat exchanger wall without creating an opening to the sub-channel of the other medium. The tunnel-like passages in the heat exchanger microstructure provided according to the invention result in a significant increase in the radial extent of the heat exchanger microstructure compared to the corrugated cross-section structure known from the prior art, since only in this way are sealed passages through a sub-channel possible without completely closing it.
[0021] The additional passages provided according to the invention, which preferably extend in ring-shaped, possibly also helical arrangements over the entire circumference of the recuperator, achieve, for example, the following advantages:
[0022] - The zones around the penetrations increase the heat exchange surfaces.
[0023] - The passages allow crossflows, which can equalize local pressure or temperature differences, among other things. - If individual sections of the channels extending around the outer circumference are blocked or narrowed by deposits, bypasses can form via the passages.
[0024] - The cross-flows created by the passages cause additional turbulence of the laminar surface layers adjacent to the heat exchanger, which positively influences the efficiency of the heat exchanger.
[0025] Preferably, the invention provides that the sub-channels of both main channels are connected in groups by point penetrations in the meandering heat exchanger wall. Firstly, the sub-channels of the feed channel are interconnected by a first group of penetrations, which allow the flow of gas towards a burner nozzle. Secondly, the sub-channels of the return channel are interconnected by a further group of penetrations, which allow the return flow of gas, in particular exhaust gas, from a combustion chamber.
[0026] The two groups of passages can be arranged with an axial offset to each other or with a radial offset at the same or only slightly offset axial position.
[0027] Because at least the heat exchanger microstructure in the recuperator according to the invention can be manufactured using a 3D printing process, a special geometric design is possible in which at least individual passages are not only designed to traverse a radial rib of the heat exchanger wall, but also to enter an intermediate zone in which two concentric, annular sub-channels for the two counter-flowing gaseous media are formed. The annular sub-channels are created in a specific axial section of the heat exchanger microstructure by the fact that the two groups of passages each extend in an annular arrangement over the entire circumference of the recuperator.If one examines the cross-sections of the heat exchanger microstructure along the axial length of the recuperator, zones with narrow, radially oriented meanders of the heat exchanger wall, resembling a star structure, alternate with zones in which both partial channels run ring-shaped and concentric to each other, being separated from each other by meandering wall sections and closed off to the inside and outside respectively, resulting in a contour comparable to the outer edge of a sunflower.
[0028] The performance and efficiency of heat transfer in the recuperator, as well as the pressure drop of the gas flow through the recuperator, can be controlled by adjusting the TPMS meander structures. Three key parameters in the mathematical model are:
[0029] - Module: Number of repetitions of the scope;
[0030] - Height (radial extent) of the meander bends, and
[0031] - Number of concentric channels, comparable to tree rings in wood.
[0032] By varying these parameters, more or less dense meander structures are created with respect to a given outer diameter or circumferential length. Dense structures increase the surface area available for heat exchange and improve the efficiency of heat recovery. Less dense structures have lower flow resistance and result in lower pressure loss, thus enabling larger volume flows of supplied combustion air and recirculated exhaust gas.
[0033] Preferably, the partial channels extend helically around the outer and inner circumferences with a steep pitch. Due to the helical shape of the partial channels, the recuperator is subjected to less stress from heating and cooling during operation than would be the case with an axially parallel arrangement. Preferably, the outer partial channels, which are used particularly for exhaust gas recirculation, are open on the outside and, in conjunction with a removable outer recuperator casing, serve as cleaning openings. The point penetrations are also easily accessible from the open partial channels.
[0034] It can also be provided that the partial channels are open on the inside and can be used as cleaning openings after the heat exchanger microstructure has been separated from an inner recuperator jacket.
[0035] The heat exchanger microstructure according to the invention requires manufacturing by an additive manufacturing process. Preferably, the entire recuperator is manufactured by an additive manufacturing process. This type of manufacturing also makes it possible to significantly reduce the wall thickness of the meandering heat exchanger wall compared to the prior art, for example to less than an average of 3 mm, whereby the wall thickness can be locally greater, particularly in the initial and final regions.
[0036] Selective laser melting enables the fabrication of metallic heat exchanger microstructures that are highly resistant to mechanical and thermal stress despite their thin walls. With a wall thickness reduced by at least half compared to the prior art, the volume available for gas flow is significantly increased, the mass of the recuperator is substantially reduced, and at the same time, the consumption of metal powder and melting energy for manufacturing is reduced.
[0037] Finally, in a particularly preferred embodiment, it can also be provided that the radial position of the passages is reversed during the alternating change between star and ring structures along the longitudinal axis. For example, in a first ring structure, the passages belonging to the feed channel are arranged on the inside of a circle, and the passages belonging to the return channel are arranged on the outside of a circle. At an axial distance from this, a plane with a star structure follows. At a further axial distance, a ring plane is followed in which the passages belonging to the feed channel are arranged on the outside of a circle, and the passages belonging to the return channel are arranged on the inside of a circle. This results in the aforementioned radial flow direction.
[0038] The return channels and feed channels for the counter-rotating gas flows formed in the heat exchanger microstructure are preferably designed as follows when viewed over the outer circumference:
[0039] - The sub-channels each have an approximately constant width along their longitudinal extent;
[0040] - They are of equal width and run parallel to each other along their length; - they each have a meandering course;
[0041] - they extend around the circumference of the heat exchanger microstructure with a steep twist.
[0042] Alternatively, it is also possible to selectively change the flow cross-sections by varying the width over the length or by using different widths of return and feed channels.
[0043] The invention is explained in more detail below with reference to the embodiment shown in the drawings and to further advantageous embodiments implemented therein. The figures show in detail:
[0044] Fig. 1 shows a recuperator in a side perspective view;
[0045] Fig. 2 shows a longitudinal section through the recuperator in a side perspective view;
[0046] Fig. 3 shows a cross-section through the recuperator in perspective view looking towards the starting area;
[0047] Fig. 4 shows a cross-section through the recuperator in a perspective view looking towards the end area; Fig. 5 shows a perspective cross-section in a section plane axially offset from Fig. 4;
[0048] Fig. 6 shows an enlarged section of Fig. 5;
[0049] Fig. 7 shows a cross-section at the same axial position as Figures 5 and 6, but from a different perspective;
[0050] Fig. 8 shows the enlarged section VIII from Figure 2;
[0051] Fig. 9 shows the enlarged section IX from Figure 2;
[0052] Figs. 11 and 12 show different cross-sectional structures at different axial positions on the recuperator, at higher or lower modulus and
[0053] Fig. 10 shows a section of a model representation of the heat exchanger microstructure.
[0054] The basic principle of the formation of a heat exchanger microstructure 3 according to the invention is explained below with reference to Figures 10 and 11.
[0055] Figures 10 and 11 each show a recuperator 100 in perspective view on the right, with a cross-sectional plane marked at two different axial positions. The corresponding sectional views through the heat exchanger microstructures 3, 3' are arranged to the left.
[0056] The respective upper left cross-section in Figures 10 and 11 shows a heat exchanger microstructure 3, 3' formed around a hollow interior 6. A heat exchanger wall 4 has a meandering profile. It can be seen that the meandering region of the heat exchanger wall 4 comprises approximately parallel, radial wall sections 43 and connecting circumferential sections 41, 42 running transversely to them, the radial wall sections 43 having at least twice the length of the transverse wall sections 41, 42. The transverse circumferential sections 41, 42 form an inner circumference 2 and an outer circumference 1. Due to the structure of the heat exchanger wall 4, an outwardly open partial channel 13 of a main channel for a first flowing medium and an inwardly open partial channel 23 for a second, counter-flowing medium are formed alternately.
[0057] The channels 13, 23, which are open to the outside or inside respectively, and the wall sections 43 separating them run approximately radially and result in a star structure.
[0058] The respective lower left cross-section shows a heat exchanger microstructure 3'. Here, the plane of passages 31, 32 is precisely affected, so that ring-shaped, concentric structures become visible in this plane, which are characterized as "sunflower-shaped".
[0059] The respective lower left cross-section in Figures 10 and 11 shows that the partial channels of one medium are traversed by short circumferential passages 31, 32, which simultaneously connect the partial channels of the other medium to each other. The resulting cross-section has a sunflower-shaped structure.
[0060] The star-shaped and sunflower-shaped cross-sections alternate repeatedly along the length of the heat exchanger microstructure 3, 3'.
[0061] Comparing the respective cross-sections in Figures 10 and 11, it becomes clear that the heat exchanger microstructure 3 in Figure 10 is denser than the heat exchanger microstructure 3' shown in Figure 11. The heat exchanger microstructure 3 in Figure 10 has, for the same diameter, more inwardly and outwardly open channels 13, 23 and intervening wall sections 43 than the heat exchanger microstructure 3' in Figure 11. As a result, the surface area available for heat exchange is larger in the heat exchanger microstructure 3 in Figure 10. Conversely, the larger cross-sections of the partial channels 13, 23 in the heat exchanger microstructure 3' shown in Figure 11 result in a lower pressure drop. Since the passages 31, 32 shown in Figures 10 and 11 are not clearly visible, reference is made to Figure 12 to illustrate the location and function of the passages 31, 32.The model representation deliberately does not depict the aforementioned continuous alternation between star-shaped and sunflower-shaped cross-sections in the heat exchanger microstructure 3, 3'.
[0062] Near the inner circumference 2, passages 31 are provided, which are shown in Figure 12 as short, tubular tunnels. The passages 31 each connect two adjacent, outwardly open partial channels 13, extending through the inwardly open partial channel 23 between them.
[0063] Near the outer circumference 1, passages 32 are provided, which are also depicted as short, tubular tunnels. The passages 32 each connect two adjacent, inwardly open sub-channels 23, extending through the outwardly open sub-channel 13 located between them. The group of passages 31 and the group of passages 32 are each arranged with a radial offset from one another and an axial offset from the other. As long as a sufficient distance is maintained between adjacent passages 31, 32 to allow flow through the sub-channels 13, 23 in the axial direction past the passages 31, 32, either only a radial or only an axial offset can be selected.
[0064] Fig. 1 shows the entire recuperator 100 again in a side perspective view. The coarse or macrostructure of the heat exchanger wall 4 is tubular. It encloses a central through-opening 6 and extends between a flange 15 in a starting region 7 and a ridge 9 in an end region 8. The counter-rotating, flow-guiding channels in the heat exchanger wall 4 are subdivided into numerous sub-channels of a return channel 10 for exhaust gas, the sub-channels being open to the outside, and into numerous sub-channels of a feed channel 20 leading to the end region 8, which have a closed wall section on the inner circumference visible here and open inwards towards the through-opening 6.
[0065] The course of the sub-channels of both main channels, i.e., the return channel 10 and the feed channel 20, over the outer circumference can be characterized in the illustrated embodiment as follows:
[0066] - The sub-channels each have an approximately constant width along their longitudinal extent;
[0067] - They are of equal width and run parallel to each other along their length; - they each have a meandering course;
[0068] - they extend around the circumference of the heat exchanger microstructure with a steep twist.
[0069] In the end section 8, the heat exchanger wall 4 terminates in a double cone, through which a ridge 9 is formed. A conical section within the ridge 9 forms an outlet opening 22 of the supply channel 20, through which fresh air is directed to a gas nozzle located to the left when the recuperator 100 is used in a recuperator burner. All sub-channels that make up the supply channel 20 open into the outlet opening 22. A burner tube, for example, connects directly to the ridge 9.
[0070] A conical section outside the ridge 9 forms an inlet opening 11 of the return channel 10. At this inlet opening 11, the incoming exhaust gas flow fans out during operation into the numerous outer sub-channels that form the return channel 10.
[0071] The inlet opening 11 is thus located outside a burner tube adjoining the ridge 9 and allows exhaust gas to be drawn in directly from the combustion chamber. For the operation of the recuperator 100, the exposed partial channels must be covered by an inner recuperator jacket on the inner circumference and by an outer recuperator jacket on the outer circumference, as only in this way are flow channels formed that are closed along the length between the inlet and outlet. The recuperator jackets are preferably simple cylindrical steel tube sections.
[0072] Fig. 2 shows the recuperator 100 in the same view as in Fig. 1, but in longitudinal section. It is clear that the outer partial channels 13, which are part of the return channel 10, are closed towards the inner circumference, while the inner partial channels 23, which are part of the feed channel 20, are open to the inside.
[0073] The section VIII marked in Fig. 2 from the end region 8 of the recuperator 100 is shown enlarged in Fig. 8. The outlet openings 22 of the partial channels 23 of the feed channel open into a cone-shaped section within the ridge 9. The inlet openings 11 of the partial channels 13 of the return channel are located in a cone-shaped section outside the ridge 9. The dashed, curved lines mark ring lines along which point penetrations 31, 32 are arranged.
[0074] The section IX marked in Fig. 2 from the initial region 7 of the recuperator 100 is shown enlarged in Fig. 9. The outlet openings 12 of the partial channels 13 of the return channel open outside the flange 15. The inlet openings 21 of the partial channels 23 of the feed channel are located inside the flange 15.
[0075] Fig. 3 is a cross-section through the recuperator 100 in a perspective view. The heat exchanger wall 4 is formed by a highly complex heat exchanger microstructure 3, which maximizes the usable area for heat exchange between the two counter-flowing fluids. The heat exchanger wall 4 has a meandering profile in the depicted section plane. It can be seen that the meandering region of the heat exchanger wall 4 comprises parallel, approximately radial wall sections and connecting circumferential sections running transversely to them, with the radial wall sections having at least twice the length of the transverse wall sections. The radial wall sections are each curved in on themselves, but nevertheless parallel to each other.
[0076] The special features of the design according to the invention are illustrated by the further perspective cross-section through the heat exchanger microstructure 3 in Figure 4. Here, the view is directed towards the section plane and the end region 8.
[0077] In the plane of section, the heat exchanger wall 4, in its meandering course, has circumferential sections 41 running along the outer circumference 1 on the outside, and further circumferential sections 42 running along the inner circumference 2 on the inside. The circumferential sections 41, 42 are each connected by the radial wall sections 43, so that an outwardly open partial channel 13 of the return channel and an inwardly open partial channel 23 of the supply channel are formed alternately.
[0078] Some of the inner circumferential sections 41 and some of the outer circumferential sections 42 are provided with spacer bosses 45, 46. These facilitate the insertion or sliding of a cylindrical recuperator jacket and prevent it from becoming jammed during operation. Additionally, the spacer bosses create a gap between the outer circumference of the heat exchanger wall 4 and the inner circumference of a recuperator jacket that can be fitted over it. Depending on the installation situation in the radiant tube of a furnace, this allows for additional heat exchange between the outer circumference of the heat exchanger wall 4 and the recuperator jacket.
[0079] The passages 31, 32 are located a short axial distance behind the section plane in Figure 4. If one focuses precisely on the two passages 31 at the top left, to which the lines of the reference numeral "31" there refer, it can be seen that these each connect two adjacent partial channels 13 for exhaust gas to each other by passing through the intermediate partial channel 23 for fresh air.
[0080] Figure 5 shows a cross-section from the same perspective as Figure 4, however, the section plane is slightly offset axially towards the end region 8 compared to Figure 4. A heat exchanger microstructure 3' exists in this section plane. This microstructure has a central wall 44 that runs in a wave-like pattern between the circumferential sections 41 and 42. Adjacent outer partial channels 13 are connected via passages 31, which are arranged on an outer track within the heat exchanger wall. Adjacent inner partial channels 23 are connected via passages 32, which are arranged on an inner track within the heat exchanger wall.
[0081] The arrangement of the passages 31 on the outer track and the passages 32 on the inner track is clearly shown in Figure 6, which is an enlargement of a section VI marked in Fig. 5.
[0082] Figure 7 shows another cross-section at the same axial position as in Figures 5 and 6, but with a slightly different perspective. Due to the altered viewing angle, one can see not only the passages 31, 32 separated by the central wall 44 in the section plane, but also that the partial channels 23, which are connected to each other in the section plane by the passages 32 on the inner track, additionally have a connection to further passages 32 that are not only deeper, but also radially further out. The deeper passages 32 are shown hatched because they only form connections between the adjacent partial channels, but are not open to the outer circumference.
[0083] This means that the passages 31 of the outer sub-channels 13 are located in some axial positions on the outer track, as shown in Figure 6, and the passages 32 of the inner sub-channels 23 are located on the inner track. In axially offset section planes, the inner and outer sub-channels 13, 23 exchange the positions of their associated passages 31, 32 from inside to outside and from outside to inside, respectively. This results in three essential flow paths being formed in each of the two counter-flowing main channels:
[0084] - a largely linear longitudinal flow along the helical course of the sub-channels, as can be seen in particular in Figure 1;
[0085] - a crossflow through the passages 31, 32, which are located one behind the other at axial positions on a circular path, as can be seen in particular in Figure 6; and
[0086] - a flow in which a flow direction along the Z-axis (central axis) is superimposed with a radial flow direction from inside to outside or vice versa, because the radial positions of the groups of passages 31, 32 alternate over the axial length of the recuperator.
Claims
KPSP 009 WO A6.docx Patent claims:
1. Recuperator (100) for gaseous media for use in an industrial gas burner, which is tubular over most of its length and has a heat exchanger microstructure (3, 3') formed by at least one heat exchanger wall (4), which has a central through-opening (6) and is covered on the inner circumference (2) by an inner recuperator jacket and on the outer circumference (1) by an outer recuperator jacket, where: the heat exchanger microstructure (3, 3') has at least two counter-rotating channels (10, 20), one of which is a return channel (10) extending between an inlet opening (11) and an outlet opening (12) and one of which is a feed channel (20) extending between an inlet opening (21) and an outlet opening (22) for a gaseous medium; the heat exchanger microstructure (3, 3') is formed by a heat exchanger wall (4) which meanders at least sectionally in cross-section, through which the partial channels (13, 23) distributed around the circumference and running along the outer circumference (1) and / or along the inner circumference (2) are formed, each of which is part of the return channel (10) or part of the supply channel (20), characterized by - that adjacent sub-channels (13, 23) of the same main channel (10, 20) are connected to each other by several point openings (31, 32) which extend through a sub-channel (13, 23) of the other main channel (10, 20) without opening towards or closing it upon passage and - that the sub-channels (13, 23) of different main channels are at least sectionally arranged in cross-section either star-shaped or concentric-KPSP 009 WO A6.docx run parallel to each other, whereby, viewed over the axial extension of the recuperator (100), the partial channels (13, 23) of different main channels transition from a star-shaped course to a concentric course or vice versa by means of the point openings (31, 32).
2. Recuperator (100) according to claim 1, characterized in that the heat exchanger microstructure (3, 3') has, in addition to the inlet and outlet openings (11, 12, 21, 22) for the channels (10, 20) on its outer circumference, further openings (8) which can be covered by a removable outer recuperator jacket.
3. Recuperator (100) according to claim 1 or 2, characterized in that the heat exchanger microstructure (3, 3') has, in addition to the inlet and outlet openings (11, 12, 21, 22) for the channels (10, 20) on its inner circumference, further openings which can be covered by a removable inner recuperator jacket.
4. Recuperator (100) according to claim 2 or 3, characterized in that the further openings are formed by partial channels which are open over a substantial part of their length on the outer circumference (1).
5. Recuperator (100) according to one of claims 2 to 4, characterized in that the further openings are formed by partial channels which are open over a substantial part of their length on the inner circumference (1).
6. Recuperator (100) according to one of the preceding claims, characterized in that the partial channels (13, 23) each extend from an initial region at the inlet opening (11, 21) of the recuperator (100) to an end region axially spaced therefrom at the outlet opening (12, 22).
7. Recuperator (100) according to one of the preceding claims, characterized in that the meandering area of the heat exchanger KPSP 009 WO A6.docx wall (4) comprises approximately parallel, radial wall sections (43) and connecting wall sections (41, 42) running transversely to them.
8. Recuperator (100) according to claim 7, characterized in that the radial wall sections (43) have at least twice the length of the transverse wall sections (41, 42).
9. Recuperator (100) according to claim 7 or 8, characterized in that the radial wall sections (43) are curved in themselves and parallel to each other.
10. Recuperator (100) according to one of the preceding claims, characterized in that the partial channels (13, 23) each have a serpentine course over their length and that adjacent partial channels (13, 23) run parallel to each other.
11. Recuperator (100) according to one of the preceding claims, characterized in that the partial channels (13, 23) extend helically around the outer and inner circumference (1, 2).
12. Recuperator (100) according to one of the preceding claims, characterized in that the partial channels of both main channels (10, 20) are connected to each other by point openings (31, 32) on the meandering heat exchanger wall (4), wherein, on the one hand, the partial channels (23) of the feed channel (20) are connected by a first group of openings (32), and, on the other hand, the partial channels (13) of the return channel (10) are connected by a further group of openings (31).
13. Recuperator (100) according to claim 12, characterized in that the two groups of passages (31, 32) are arranged with an axial offset from each other and / or with a radial offset at the same or only slightly offset axial position. KPSP 009 WO A6.docx 14. Recuperator (100) according to one of the preceding claims, characterized in that the heat exchanger microstructure (3, 3') comprises a complex channel system in which the return channel (10) and the feed channel (20) are each divided into a plurality of small sub-channels (13, 23) and are joined together again in an end region.